Hydrolysis of biomass using supercritical water is a complex process. In addition, the biomass is a complex material containing polymeric saccharides, aromatic polymers, organic acids, extractives, ash, and the like. Supercritical fluids, including supercritical water, have solubility, reactivity, density, and viscosity that are different from the same fluid in subcritical form. The use of supercritical water to hydrolyze the polymeric saccharides has been found to be a cost-effective way to produce cellulosic sugars for use, inter alia, in biofuels and industrial biochemicals.
When processing biomass with high temperature fluids, such as a supercritical fluid, fouling can occur on the walls of the reaction vessels, such as tubular reactors. This fouling builds up over time, constricting the flow path and eventually leading to high pressure drops and reduced vessel volume. One common approach to address the problem is to take the reaction vessel offline and manually clean it with brushes and/or chemicals (e.g., caustic). While this approach works for some applications, it unfortunately involves stopping production of that particular reactor for the period of the cleaning. This can result in either higher capital costs (if multiple reactors or arrays are utilized to compensate for the down time), reduced throughput (less material produced per annum due to downtime), or both.
Thus, there is an ongoing need for methods that clean the system with minimal or essentially no down time and, preferably, without the addition of exogenous chemicals. The methods disclosed herein are directed toward these, as well as other, important ends.